1. Field of the Invention
This invention relates to a controlling apparatus for a motor vehicle having a high voltage direct current (dc) power supply, an inverter for converting dc power of the high voltage dc power supply into ac power, a smoothing capacitor provided between the inverter and the high voltage dc power supply, a main contactor provided between the high voltage dc power supply and the smoothing capacitor for connecting and disconnecting the high voltage dc power supply and the smoothing capacitor to and from each other, and a precharge circuit connected in parallel to the main contactor.
2. Description of the Related Art
In motor vehicles such as a hybrid vehicle, a fuel cell vehicle and an electric automobile, driving force is generated by a generator-motor (hereinafter referred to as electric motor or motor) and transmitted to an axle. In order to obtain optimum driving force in response to a traveling state of the vehicle, a voltage of a high voltage battery (high voltage dc power supply) is subjected to direct current/three-phase alternating current conversion by an inverter to obtain driving force of the motor. Further, kinetic energy transmitted from the axle to the electric motor is converted into electric energy, subjected to three-phase alternating current/direct current conversion by the inverter and regenerates the direct current to the high voltage battery. In order to connect and disconnect the high voltage battery and the inverter to and from each other, a main contactor of a mechanical relay is provided. Further, a smoothing contactor is provided in order to smooth the primary power supply and suppress a surge voltage to protect the device.
When an ignition switch is switched ON, if the main contactor is switched ON to charge the smoothing capacitor, then the smoothing capacitor is damaged by rush current, and therefore, in order to prevent the damage and prevent adhesion of the main contactor, the smoothing capacitor is pre-charged.
Further, if the main contactor is ON when a great potential difference appears between the smoothing capacitor and the high voltage battery upon regeneration, then an over-voltage is applied to the high voltage battery and the life of the high voltage is shortened, and therefore, the main contactor is switched OFF to allow discharge from the smoothing capacitor to the high voltage battery through the pre-charge circuit.
Therefore, bidirectional energization for charge from the high voltage battery to the smoothing capacitor and discharge from the smoothing capacitor to the high voltage battery is demanded for the pre-charge circuit. Conventionally, Japanese Patent Laid-Open No. Hei 09-056167 and Japanese Patent Laid-Open No. 2006-304408 are available as prior art documents relating to precharge of a smoothing capacitor.
It is disclosed in Japanese Patent Laid-Open No. Hei 09-056167 that, before a main contactor 3 is switched on, a precharge contactor 5 is switched on to precharge a smoothing capacitor 6 from a high voltage battery 1 through a current limiting element (resistor) 4 and the mechanical precharge contactor 5.
It is disclosed in Japanese Patent Laid-Open No. 2006-304408 that a precharge circuit is formed from a system main relay SMR1 formed from a semiconductor relay of the FET (field-effect transistor) type and a limiting resistor R to carry out precharge and, upon regeneration, a high voltage is charged from a smoothing capacitor C by another system main relay SMR2.
However, in Japanese Patent Laid-Open Hei 09-056167, there is a problem that the cost is high because the precharge contactor is a mechanical relay. Further, there is another problem that, since a precharge resistor is externally connected, the circuit scale is increased.
Meanwhile, in Japanese Patent Laid-Open No. 2006-304408, although a system main relay of the FET type is used only for the precharge from the high voltage battery to the smoothing capacitor, it is necessary to allow bidirectional energization in order to discharge from the smoothing capacitor to the high voltage battery as described above. Where the bidirectional energization is carried out by a semiconductor switch of the FET type, a semiconductor relay is required individually for charge from the high voltage battery to the smoothing capacitor and discharge from the smoothing capacitor to the high voltage battery, and there is a problem that the cost becomes high.